1. Field of the Invention
The present invention relates to a temperature sensor, a temperature control device and a temperature controller that include the temperature sensor, and a method of temperature control, particularly to a temperature sensor, a temperature control device, a temperature controller and a method of temperature control for a semiconductor wafer.
2. Description of Related Art
In recent years, along with demands for a performance enhancement and a cost reduction of semiconductor devices, there have been demands for a miniaturization, an improvement of yield, an improvement of throughput and a high-mix low-volume manufacturing in manufacturing processes of semiconductor devices. In order to meat these demands, a high accuracy is required in a circuit linewidth. The accuracy of the circuit linewidth depends on a wafer temperature inside a chamber in a heat treatment process. Accordingly, in the manufacturing processes of the semiconductor devices, it has been important to maintain the wafer temperature in the heat treatment process at a predetermined value. For example, in photolithography, the wafer temperature is controlled by adjusting a temperature of a hot plate for heating the wafer and a temperature of a cooling plate for cooling.
Particularly in photolithography, a chemically-amplified resist agent used for forming a linewidth of 150 nm or below is vulnerable to an influence of temperature changes. The linewidth formed using the resist agent largely depends on a heating temperature in a post exposure bake (PEB) treatment after exposure. When the chemically-amplified resist agent is used, a uniformity of in-plane temperature distribution of the wafer is required to be within ±0.1° C. in a steady state of the PEB treatment, whereby a distinctly high accuracy is required. In order to meet such demands, a temperature sensor is also required to secure a measurement accuracy of the same level.
For example, as shown in FIG. 16, in photolithography, a wafer 50 is mounted on a hot plate 1, such that a heater 3 provided in the hot plate 1 heats the wafer 50. At that time, in order to prevent a back surface of the wafer 50 from being contaminated by contacting a plate body 4 forming the hot plate 1, the wafer 50 is mounted on the hot plate 1 via a support pin 5 provided on the plate body 4. In order to enhance a responsivity of the wafer 50 to a temperature adjustment of the hot plate 1, a height dimension of the support pin 5 from a surface of the plate body 4 is set at a distinctly small value of approximately 0.1 mm.
In this state, a uniformity of an in-plane temperature distribution of the wafer 50 mounted on the hot plate 1 is adjusted by a multivariable control of the heaters 3 using a measurement value of temperature sensors 90 embedded in a plurality of points of the plate body 4 (e.g., Document 2: JP-A-2001-230199). In this case, since an actual temperature of the wafer 50 to be controlled is unknown, there is a difficulty in accurately performing a temperature control of the wafer 50.
Accordingly, in order to obtain the actual temperature of the wafer 50, there has been developed a temperature sensor that directly measures the temperature of the wafer 50 by contacting the wafer 50 inside the chamber (e.g.: Document 1: JP-A-2003-100605; Document 3: JP-A-07-221154; Document 4: JP-A-04-148545; Document 5: JP-A-04-51538; and Document 6: JP-UM-A-62-47124).
In addition, there has been a demand for a temperature controller for controlling a temperature of a wafer based on a measurement value of a temperature sensor, which is obtained by measuring an actual temperature of the wafer by bringing the temperature sensor into contact with the wafer.
However, the temperature sensor according to Document 1 is directly attached to a spherical spacer on a heating plate, and heat of the heating plate is conducted to the temperature sensor via the spacer. Thus, the temperature sensor is influenced by the heat of the heating plate in measuring the temperature, whereby a measurement accuracy of the wafer temperature is not sufficiently secured.
In the temperature sensor according to Document 3, a support pin made of silica glass supports a thermocouple, and an alumina cap bonded with the thermocouple is provided at a tip end of the support pin. However, since silica glass forming the support pin has a high heat conductivity of approximately 1.4 W/mk and a diameter of the support pin is as large as 2.5 to 3.5 mm, a large amount of heat is conducted to the support pin from the wafer. Accordingly, the measurement accuracy of the wafer temperature is not sufficiently secured. In actuality, Document 3 recites that a measurement error of the temperature sensor is approximately several degrees (° C.).
In addition, since the diameter of the cap surface contacting the wafer is as large as 4 mm, a large amount of heat is discharged from the wafer via the cap, whereby the uniformity of the in-plane temperature of the wafer may be influenced.
In the temperature sensor according to Document 4, since an outer diameter of a rod-like cover member that covers the thermocouple is as large as approximately 0.5 to 0.8 mm, when a space between the wafer in a mounting state and the plate is set at approximately 0.1 mm, the temperature sensor cannot be disposed within the space. Even if the temperature sensor is disposed, since a tip end of the cover member that contacts the wafer is a flat surface of approximately 0.5 mm width and a contact area with the wafer is large, a large amount of heat is discharged from the wafer, whereby a uniformity of an in-plane temperature of the wafer may be influenced.
In the temperature sensor according to Document 5, since a support pin for supporting a metal thin film is much larger than the metal thin film, a large amount of heat is discharged to the support pin. Accordingly, the measurement accuracy of the wafer temperature is not sufficiently secured.
In addition, since the large amount of heat is discharged to the support pin, a uniformity of an in-plane temperature of the wafer may be influenced.
In the temperature sensor according to Document 6, a spring fixed to a heater is mounted with a circular disc that contacts the wafer, and the circular disc is mounted with a thermocouple. With this arrangement, the heat of the heater is conducted to the thermocouple via the spring and the circular disk, such that the thermocouple may be influenced by the heat of the heater in measuring the temperature. Accordingly, the measurement accuracy of the wafer temperature is not sufficiently secured.
In addition, since an area of the circular disc with which the disc contacts the wafer is large, a large amount of heat is discharged from the wafer to the spring and the circular disc, whereby a uniformity of an in-plane temperature of the wafer may be influenced.
When the wafer temperature is measured by bringing the temperature sensor into contact with the wafer, the temperature sensor directly contacts a gas inside the chamber, unlike an arrangement of Document 2 in which the temperature sensor is embedded in the plate body. Accordingly, the measurement value of the temperature sensor is greatly fluctuated due to an influence of a natural convection arising on the hot plate before the wafer is mounted, and a control command for the hot plate is also fluctuated in accordance therewith. In this case, the temperature of the hot place is also largely fluctuated in accordance with the control command, whereby a subsequent temperature control may not be smoothly performed.